BIND 10 #536: Make OutputBuffer more lightweight

[BIND 10 Development]

#536: Make OutputBuffer more lightweight
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           Reporter:  vorner         |                      Owner:  jinmei
               Type:  task           |                     Status:  new
           Priority:  major          |                  Milestone:  A-Team-
          Component:  DNSPacket API  |  Sprint-20110209
          Sensitive:  0              |                   Keywords:
Add Hours to Ticket:  0              |  Estimated Number of Hours:  0
        Total Hours:  0              |                  Billable?:  1
                                     |                  Internal?:  0
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 This is one of the performance related tasks.

 The isc::dns::OutputBuffer::operator[] function takes 25% of our running
 time. It is quite surprising, as a simple function like that should
 inline. The task is to make it more friendly for inlining, which includes:
  * The return value of the operator[] should be uint8_t instead of const
 uint8_t &, because the single byte is smaller to copy/pass around than
 actual pointer and saves overhead of taking the address and dereferencing
 it.
  * The data inside should be kept if something simpler than vector (as
 this is the probable reason why it isn't inlined). An array should be
 enough. It is more work to do in the modifying functions, and care must be
 taken to correctly allocate/deallocate (and create a copy constructor, if
 one is needed anywhere), but the possible performance gain should be
 large.

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Ticket URL: <https://bind10.isc.org/ticket/536>
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